Where there's a will there's a way 2x RTX 3090

Wow system requirement recommended 

DirectX® 12 capable 8 GB GPU NVIDIA® GeForce® RTX which includes 2080 or 3060 or higher 

D4 recommended NVIDIA GeForce GTX 460 or ATI Radeon HD 6870 or better, which is much lower than WoW.

therefore if you have a stock dell gtx gpu you can consider rtx 2080, 2080ti, 3060 or higher depending on your budget for those games.

note R2 cpu is old and will bottleneck high end RTX gpu significantly 

benchmatk if cpu is i7-3820 in R2

benchmark if cpu is i7-4960x

To make a long story short, it will not be economical to upgrade that machine for WoW/Diablo4 with the best settings.

If you want the best settings, a complete new machine is the only economical system upgrade. Your best option for that would be to look for holiday deals, if you can afford it.

Otherwise there's not much I can recommend, unless you can find a cheap second hand 1070 GTX or something like that. But that comes with it's own risks since it would be a used card. You would also have to make sure your power supply supports any GPU upgrades, and as mentioned below you are likely going to run into a CPU bottle neck.

What components do you currently have in your rig?

Unless I missed it, your post doesn't say what components or video-card are inside it now, so not sure how we can advise you on which 1-2 components to upgrade.

I can tell you that system requirements for WoW and especially Diablo-4 are very low. Based on previous experience, I can tell you a normally configured Aurora-R6, with just an SSD, Intel-i7, 16gb ram, and GTX-1070 can easily run those.

@Real_Boy85​ i need to reach out to you as i have the same r2, but only one single 970 currently and was looking to go for rtx but i didnt believe they could be compatible besides psu

@kilomikemike​   most any graphics card will be compatible . . . your CPU could become a bottleneck.

@ProfessorW00d​ exactly, i still run the stock 5820 i7, was looking to see if i can still upgrade in this existing MOBO without getting a new msi and new cpu

@kilomikemike​ yes, you can upgrade the graphics card. How much of a bottleneck your CPU will be will depend on many factor, to include the specific game, and resolution. If you play GPU intensive games, CPU bottleneck may not have a big affect.